I'm wondering whether the speech bubbles should have softer edges, they still seem a little detached from the image.Why don't you scan some painted speech bubbles or cut out textured card, change the opacity and maybe have a fiddle with different layer modes such as overlay and multiply.
What I'd love to do if I had the time is handmake all speechbubbles so they properly fit what's going on, then add the digital lettering on top.Atm I haven't really... got that time. :P but yeah. I know what you mean. It's really hard. :(Deffo gonna play with this page more. Maybe tonight!